Mirror modifier not working correctly
If I'm not wrong I think you mean the middle section where the mirror is?
It looks like you may have a face at that middle section. Just delete it and it will stick together instead of creating two separate sections

There are hidden faces hidden in the middle section.

Press Z to select the face.

The Mirror Modifier automatically merges the vertices if the option to merge is turned on. No longer having a separate section.
Hope this helps! Enjoy your modeling ;)